Drugs and other compounds intended for use in the diagnosis, cure, mitigation, treatment or prevention of disease in man or other animal or for use in the agricultural arena, have made a significant impact on the practice of modern medicine and on the agricultural arena. In some cases, such as in the development of vaccines, drugs have essentially eradicated once untreatable diseases. In the case of the agriculture, compounds have been developed which both extend the life and/or volume of produce as well as kill unwanted plants where desirable. Therefore, the development of these compounds is of great interest.
Many useful compounds modulate the physical interaction of proteins. Traditionally, these protein—protein interactions have been evaluated using biochemical techniques, including chemical cross-linking, co-immunoprecipitation, co-fractionation and co-purification. Recently genetic systems have been invented to detect protein—protein interactions. The first work was done in yeast systems, and was termed the “yeast two-hybrid” system. The basic system requires a protein—protein interaction in order to turn on transcription of a reporter gene. Subsequent work was done in mammalian cells. See Fields et al., Nature 340:245 (1989); Vasavada et al., PNAS USA 88:10686 (1991); Fearon et al., PNAS USA 89:7958 (1992); Dang et al., Mol. Cell. Biol. 11:954 (1991); Chien et al., PNAS USA 88:9578 (1991); and U.S. Pat. Nos. 5,283,173, 5,667,973, 5,468,614, 5,525,490, and 5,637,463.
In another approach to drug discovery, studies are designed to determine the biological activity of a protein. For example, the conditions such as the specific substrate or stimulator required for an enzymatic reaction are investigated. Moreover, there are a number of studies designed specifically for aide in the detection step in these assays. For example, one study discloses a spectrophotometric assay for inorganic phosphate (Pi) to probe the kinetics of Pi release from biological systems such as GTPases and ATPases. Webb, PNAS, 89:4884–4887 (1992). Another study reports on an enzymatic assay of inorganic phosphate in serum using nucleoside phosphorylase and xanthine oxidase. Ungerer, et al., Elsevier Clinica Chimica Act, 223:149–157 (1993). A continuous spectrophotometric assay for aspartate transcarbamylase and ATPases is reported on in Rieger, et al., Anal. Biochem., 246:86–95 (1997). There is also a study which reports on the measurement of inorganic phosphate release using fluorescent probes and its application to actomysin subfragment 1 ATPase. Brune, et al., Biochem., 33:8262–8271 (1994). U.S. Pat. No. 4,923,796 discloses a method for quantitative enzymatic determination of ADP. Microtubule-stimulated adenosine triphosphate (ATP) hydrolysis by kinesin is discussed in Hackney, J. Biol. Chem., 269(23):16508–16511 (1994). Furthermore, enzymatic fluorimetry and fluorimetric assays for ATPase activity are reported on in Greengard, Nature, 178:632–634 (1956) and Utpal and Siddhrtha, Biochem. J., 266:611–614 (1990), respectively.
In a different approach, modulators of an enzymatic reaction are investigated, wherein the conditions which allow the enzymatic reaction to occur are already known. For example, U.S. Pat. No. 5,759,795 discloses an assay for identifying an inhibitor of a Hepatitis C Virus NS3 protein ATPase which involves a luciferase reaction. Luciferase reactions are known in the art. In the case of an ATPase inhibitor, the presence of an ATPase inhibitor is indicated when ATP is available to drive the oxidation of luciferon by luciferase. This approach requires ATP but does not re-generate ATP.
Thus, while efforts have been made toward drug discovery, more efficient means are desirable. In particular, there is a need for an efficient system which can distinguish between a compound directly binding to a second component, or whether the compound modulates the binding between two other components, or whether the compound modulates the biological activity of a known enzymatic reaction. Accordingly, it is an object of the present invention to provide methods of identifying compounds which either bind to or which modulate the binding characteristics or the biological activity of a target protein. It is also an object to provide compositions for use in the assays provided herein.